CTE was first identified in boxers and then in athletes who took part in other sports where blows to the head are common, such as American football and wrestling.

The proposed reason for injury was repeated heading of the ball. The researchers estimate a professional footballer playing in positions like central defence or centre forward will head the ball at least 2,000 times over the course of their career.

While these results sound concerning, this was a small descriptive study and hasn’t proved repeated headers were the cause of the brain damage seen in the players.

As Dr David Reynolds of Alzheimer’s Research UK pointed out, the benefits of regular exercise in terms of dementia prevention may well outweigh any risk, especially for those who play football on a recreational basis.

A large study following up footballers without dementia is now needed to see who develops the condition.

Comparisons can then be made between those with and without dementia, which may be able to identify risk factors like frequency of heading.

As for the question asked by the Daily Mirror, like most headlines that end in a question mark, the answer is likely to be “we don’t know”.

Where did the story come from?

The study was carried out by researchers from University College London, Cardiff University and the Cefn Coed Hospital in Swansea.

It was funded by the National Institute for Health Research and the Drake Foundation, a not-for-profit organisation set up in 2014 to fund research into concussion injuries in sport.

The study was widely covered in the UK media. While some of the headlines were possibly alarmist, the actual body of the reporting was well balanced.

For example, the Daily Mirror included a column from the lead author of the study, Dr Helen Ling, who said: “It is important to note we studied only a small number of retired footballers with dementia and still do not know how common dementia is among footballers.

“The most pressing question is now to find out if dementia is more common in footballers than in the normal population.”

What kind of research was this?

This was a case series study where a small number of football players who already had dementia were clinically assessed over a long period of time.

Case series are not able to show an association because all the participants already have the condition and there is no comparison group.

This means researchers are not able to account for other possible causes or confounding factors. They are useful types of studies for generating hypotheses that can then be assessed in larger cohort studies.

These larger cohort studies typically involve a large number of people in the population without a condition who are followed up over time to see who develops it. Comparisons can then be made between people with and without the condition.

Cohort studies tend to be large enough to be able to show an association between certain factors – for example, frequent football heading and brain damage – but they cannot prove one factor causes another.

What did the research involve?

Fourteen retired footballers with dementia were regularly clinically assessed by a psychiatrist between 1980 and 2010 until they died. The next of kin of six of the players agreed for them to have a post-mortem brain examination.

In 2015-16 the researchers obtained the following information from the players’ medical notes and through interviews with close relatives:

football playing career – position and years spent playing

other sports

military service

number and severity of any concussions

medical history

family history

dementia history – age at onset and symptoms

What were the basic results?

Symptoms of dementia began at an average age of 64 years in the retired footballers.

Thirteen had been professional footballers and one was described as a committed amateur. They had started playing football in childhood or their early teens, and on average played for 26 years.

All were reported to have been skilled at heading the ball. Six footballers were reported to have had one concussion each, five of them with loss of consciousness.

These five cases had a post-mortem examination. One of these men was also an amateur boxer.

The post-mortem examinations found all six men had Alzheimer’s disease and deposits of a protein called TDP-43, which is found in motor neurone disease (MND).

All six also had some features of CTE. Four of them fulfilled the criteria for CTE diagnosis.

Some of them also had features of other neurological conditions, including vascular dementia, where symptoms occur when the brain is damaged because of problems with blood supply to the brain.

How did the researchers interpret the results?

The researchers made it clear that no firm conclusions could be drawn from this type of study.

They call for “large-scale case-control studies” comparing people who play football with athletes without increased risk of repetitive head impact.

They recommend that repeated clinical assessments over time should include high-tech brain imaging, psychological tests, genetic data and samples of cerebrospinal fluid (CSF).

Conclusion

There is growing concern that repeated concussion in contact sports like American football and rugby increase the risk of CTE, which was first found in boxers.

This study raises questions as to whether less severe but repeated head impacts, such as those sustained by heading a football, could lead to brain damage later in life.

All six of the retired footballers who had a post-mortem showed features of CTE, but the study is not able to show that this was a result of heading footballs.

As CTE can only be diagnosed at post-mortem, it has been difficult to study the progress of the condition with any degree of accuracy.

We don’t know how many people develop CTE, whether some people are more genetically susceptible, and what level and type of brain injury is required to cause the development of CTE over time.

The relationship between CTE and development of dementia also remains unclear.

The results of this study are interesting and will hopefully spark much needed larger cohort studies.